Recommendation for prototype CM (BGA reflow, mainly)

Tin-foil, a heat-gun and a sacrificial apprentice :-p

I've used Invotech for low volume production runs and they were mostly OK with BGA and are a lot better now (I think we were used as guinea pigs.) If you talk about approx 1K volumes you might be able to wangle two or three development boards for free to prove their processes.

I don't even need the tinfoil for this, as there are no other parts on the board - however my success rate with this method has been I've used Invotech for low volume production runs and they were mostly OK

I'll check them out, however I don't want to lie to anyone - the 1K is very much a maybe.

Just a steel plate with 25mm x 25mm square hole. I am thinking about the same. Unfortunately, mime is 35mm x 35mm; otherwise, we could share the stencil.

That's expensive, even if you have 10 layers. Are you counting setup costs?

By the way, in productions, would you be mounting the BGA first, or last? I am thinking about mount it last, but the stencils are more tricky to make.

You would use one of the self-adhesive BGA template things inside that hole?

175 is for the protos, which are just going to be made in 4-off (3 to be stuffed, one to buzz out problems). It's an 8-layer board. In production it would be much cheaper of course but I have to assume at least one spin between proto and production.

This is the kind of detail I would expect a CM to solve; if I contract out assembly, they would make the stencil(s) and handle the details of that nature.

Actually, no. I was thinking about the hole for existing mounted part. For the current mounting, you do need a stencil for 300+ holes for you and 475 for me.

It would not be much more to build additional boards, since the costs are for the films and masks. You can always reuse the BGAs, but not the PCBs. Especially, if you are using prototype qualities PCBs.

Then you would have to send out all the parts in advance.

We don't want to stock the BGAs and QFPs. So we are going to stuff everything else at once, and mount the CPU (475 balls) and Flash (64 balls) last. We need cut-outs (square holes for the mounted parts) and perhaps covers for them as well.

Hmm, I think I understand now. Different terminology. To me the "stencil" is the device that exposes lands you wish to receive solder paste. The plate you're talking about is what I would call a "screen".

I don't have the equipment or technique to reball BGAs, though.

Right. Normally when I've worked with a CM, the CM has sent me a list of the standard jellybeans they stock. I go down the list and see if any of their standard parts can be used in certain spaces on my board (for instance, if I have 0603 1/16W 10K pullups all over the place, I don't care what the vendor is, probably - but if I have a 5nH inductor in an RF circuit, it might be very important to have relay-wound or ceramic, and substitutes might not be OK).

Anything I want that's special or otherwise not a standard part from the CM, I buy and send to them along with gerbers and drill/route dwgs.

I don't want to stock them either - I want to have either nothing in my hands, or complete boards. I don't want to have WIP boards; what are you saving there, exactly? Not understanding your workflow :) Since you have to buy the micro and flash to build the boards anyway, what good are partial boards to you - why not just send everything to the CM at once whenever you need a build?

For me, they are different phases of stencils. I need one to first mount other SMDs except BGAs, then another one to mount the BGAs while covering the rest.

You can send out a batch of BGAs to reball them.

We want to make 500 to 1000 boards with everything else but BGAs. The Processor ($40) and Flash ($20) are too expensive right now. So, we are only mounting 100 of them at a time. Furthermore, we are still waiting for the next generations of Processor and Flash, in the coming months.

Not if they are not yet available and/or too expensive.

With properly made stencils, we might not have to send it out for the BGAs.

Hmm, and you're absolutely certain that the new generations will be

100% pin compatible, and you won't need to change any passives on the board?

I think so. The client just want 1 of everything (probably over-speced anyway). Namely, 1G CPU, 1G SDRAM and 1G FLASH. The current CPU is

66%, SDRAM is 50% and FLASH is 10%. Next Gen CPU might be 70% to 80%. We just need to add one more address trace for 1G SDRAM. There is no way to build with 1G NOR flash, so we are adding NAND flash to make it up. Anyway, these components cost more than the PCBs (approx $20 to $30), so we want to defer buying them as much as possible.

Back to the original issue of mounting BGAs last. I think the best way is to make a heat shield for all other components except the BGAs. Make an aluminium heating pad (and heating coil) below the BGA balls. Apply solder paste with a stencil. Pre-heat the board in the oven. Put the BGAs in place and burn it with the aluminium heating pad for 10 seconds.

For our prototypes, we need to first mount some QFPs (they are actually CPLDs temporary used for board testings) before the BGAs. We can do the same as in productions. First of all, we need to design and custom build some stencils and heaters.

Circuit Technology Center

have done a number of BGA re-works for me (including re-balling, removal, re-fitting, X-ray inspection etc) I was happy with quality and price.

Hi Gary,

Great. According to their online price list, the most expensive it could possibly get is $110 per board which is an acceptable price. Thanks a lot for the recommendation.